The present invention relates generally to porous polymeric particles for drug delivery to the pulmonary system.
Biodegradable polymeric particles have been developed for the controlled-release and delivery of protein and peptides drugs. Langer, R., Science, 249: 1527-1533 (1990). Examples include the use of biodegradable particles for gene therapy (Mulligan, R. C. Science, 260: 926-932 (1993)) and "single-shot" vaccine delivery (Eldridge et al., Mol. Immunol., 28: 287-294 (1991)) for immunization. Protein and peptide delivery via degradable particles is restricted due to low bioavailability in the blood stream, since macromolecules and/or microparticles tend to poorly permeate organ-blood barriers of the human body, particularly when delivered either orally or invasively.
Aerosols for the delivery of therapeutic agents to the respiratory tract have been developed. The respiratory tract includes the upper airways, including the oropharynx and larynx, followed by the lower airways, which include the trachea followed by bifurcations into the bronchi and bronchioli. The upper and lower airways are called the conductive airways. The terminal bronchioli then divide into respiratory bronchioli which then lead to the ultimate respiratory zone, the alveoli, or deep lung. Gonda, I. "Aerosols for delivery of therapeutic and diagnostic agents to the respiratory tract," in Critical Reviews in Therapeutic Drug Carrier Systems, 6: 273-313, (1990). The deep lung, or alveoli, are the primary target of inhaled therapeutic aerosols for systemic delivery.
Inhaled aerosols have been used for the treatment of local lung disorders including asthma and cystic fibrosis (Anderson, et al., Am. Rev. Rev. Respir. Dis., 140: 1317-1324 (1989)) and have potential for the systemic delivery of peptides and proteins as well (Patton and Platz, Advanced Drug Delivery Reviews, 8: 179-196 (1992)). However, pulmonary drug delivery strategies present many difficulties for the delivery of macromolecules; these include protein denaturation during aerosolization, excessive loss of inhaled drug in the oropharyngeal cavity (typically exceeding 80%), poor control over the site of deposition, irreproducibility of therapeutic results owing to variations in breathing patterns, the quick absorption of drug potentially resulting in local toxic effects, and phagocytosis by lung macrophages.
Local and systemic inhalation therapies can often benefit from a relative slow controlled release of the therapeutic agent. Gonda, I., "Physico-chemical principles in aerosol delivery," in: Topics in Pharmaceutical Science 1991, D. J. A. Crommelin and K. K. Midha, Eds., Stuttgart: Medpharm Scientific Publishers, pp. 95-117, 1992. Slow release from a therapeutic aerosol can prolong the residence of an administered drug in the airways or acini, and diminish the rate of drug appearance in the blood stream. Also, patient compliance is increased by reducing the frequency of dosing. Langer, R., Science, 249: 1527-1533 (1990); and Gonda, I., "Aerosols for delivery of therapeutic and diagnostic agents to the respiratory tract," in Critical Reviews in Therapeutic Drug Carrier Systems, 6: 273-313, 1990.
The human lungs can remove or rapidly degrade hydrolytically cleavable deposited aerosols over periods ranging from minutes to hours. In the upper airways, ciliated epithelia contribute to the "mucociliary excalator" by which particles are swept from the airways toward the mouth. Pavia, D., "LungMucociliary Clearance," in Aerosols and the Lung: Clinical and Experimental Aspects, Clarke, S. W. and Pavia, D., Eds., Butterworths, London, 1984. In the deep lungs, alveolar macrophages are capable of phagocytosing particles soon after their deposition. Warheit, M. B. and Hartsky, M.A., Microscopy Res. Tech., 26: 412-422 (1993); and Brain, J. D., "Physiology and Pathophysiology of Pulmonary Macrophages," in The Reticuloendothelial System, S. M. Reichard and J. Filkins, Eds., Plenum, N.Y., pp. 315-327, 1985. As the diameter of particles exceeds 3 .mu.m, there is increasingly less phagocytosis by macrophages. However, increasing the particle size also minimizes the probability of particles (possessing standard mass density) entering the airways and acini due to excessive deposition in the oropharyngeal or nasal regions. Heyder, J., et al, J. Aerosol Aci., 17: 811-825 (1986). An effective slow-release inhalation therapy requires a means of avoiding or suspending the lung's natural clearance mechanisms until drugs have been effectively delivered.
Therapeutic dry-powder aerosols have been made as solid (macroscopically nonporous) particles, with mean diameters less than approximately 5 .mu.m to avoid excessive oropharyngeal deposition. Ganderton, D., J. Biopharmaceutical Sciences 3: 101-105 (1992); and Gonda, I., "Physico-Chemical Principles in Aerosol Delivery," in Topics in Pharmaceutical Sciences 1991, Commelin, D. J. and K. K. Midha, Eds., Medpharm Scientific Publishers, Stuttgart, pp. 95-115, 1992.
There is a need for improved inhaled aerosols for pulmonary delivery of therapeutic agents. There is a need for the development of drug carriers which are capable of delivering the drug in an effective amount into the airways or the alveolar zone of the lung. There further is a need for the development of drug carriers for use as inhaled aerosols which are biodegradable and are capable of controlled release within the airways or in the alveolar zone of the lung.
It is therefore an object of the present invention to provide improved carriers for the pulmonary delivery of therapeutic agents. It is a further object of the invention to provide inhaled aerosols which are effective carriers for delivery of therapeutic agents to the deep lung. It is another object of the invention to provide carriers for pulmonary delivery which avoid phagocytosis in the deep lung. It is a further object of the invention to provide carriers for pulmonary drug delivery which are capable of biodegrading and releasing the drug at a controlled rate.